H2 Physics Practical (2)

H2PhysicsPractical Preparation● Bringcurveruler Settingup● Experimentsinvolvingstring○ Tyingknots○ Step1isalwaystomaketoothinstringthicker,so2plyit.○ Ifuwantstringtobemovable,1knotwilldo○ Ifuwantstringtobeunmovable,donottieadeadknot.Method1:1knotbyhangingstringaroundtautstring,followedby1knotbytautstringaroundhangingstring.○ Alternatively,clovehitch:suitableforbothmovableandunmovablepurposes.2clockwiseloops. ● Retortstand○ Noteperspectiveasdrawnindiagram○ Seeifursupposedtohangstufffromthebossorfromtheclamp○ Bossisthesmallthingthatisattachedtotheretortstandneckdirectly○ Clampistheadditionalthingkiapedontotheboss,hasarodandhaspincers ● Circuits○ Multimetersusedasammetersaresetuptogetherwithcircuitcuzitispartofthecircuit

○ Multimetersusedasvoltmetersaresetupattheveryendcuzitisalonewolf○ Multimetersusedasresistor:startwithlowestresistancesetting.“1.”meanssettingistoolow.Turnitup. Measurements● Length○ Maynotalwaysbeverniercaliper.Istheobjectsmallenough?Ruler.○ Verniercaliper■ Zeroerror=0.00cm(2dp)● Repeatif:○ Recordingtime○ Usingverniercaliper/micrometerscrewgauge○ Largepossibleerror■ Egflimsyobject■ Egnonuni-dimensional,differentpartsofobjecthavedifferentdimensions○ 2marks● Noneedtorepeatif:○ 1mark○ Smallsmallpossibleerror■ Eglengthofsmt■ Electricalexperiments● Remembertowriteyourunits● Record=/=measure.Recordmeanstakethevaluethatqntellsyou. Apparatus● Multimeter○ Knowhowtoproblem-solvethisdevil○ Ifusedtomeasureresistance,itshouldbeconnectedtoresistorwithoutcurrentflow.(cuzmultimetermeasuresresistancebyinjectingcurrent.Won’tworkproperlyifthereisalreadycurrent!)○ Hmeanshold.Pressbutton.○ Batterymeanslowbattery.○ 1meansbigvalue,setupwrong.

○ 0meanschangemultimeter.○ SettingsarecorrectlysetforuinAlevels.Don’tchange.● Micrometerscrewgauge○ Don’tover-tightenit.Turnthimble→makecontactwithobject→turnratchet→3clicksenough.● Verniercaliper○ Thingstickingoutiscalled“depthprobe”. Calculationsandcommonerrorsbyyourstruly ● Uncertainty○ Absoluteuncertainty■ Precisionofinstrumentmultipliedby3-5duetoexpterror● Ifmax-minmethod/mathematicalmethodgivesbiggerabsuc,useitinstead.■ Thismultiplicationisnotshowneg ∆𝑡𝑡 = 3𝑤ℎ𝑎𝑡𝑒𝑣𝑒𝑟 𝑥 100%■ Rememberx100%■ 1sf■ Fortime:absoluteucjustwrite3■ Length:0.1cmx3=0.3cm■ Noneedx3formeasurementsofdiameter.Nohumanerror.○ Percentageuncertainty■ leftto2sf■ Writtenas__%,notasadecimal○ Chooseavalueof(variable)touseinfollowingexperiments■ Concepttested:uncertainty■ “Absoluteuncertaintyislarge.Toreducepercentageuncertainty,valueischosentogivelargestvalue” ● Calculatingconstants○ Followsfanddprules○ Otherthanlookingatsubstitutedvaluestofindthesmallestsf,seeiftheexpressionforconstantonlyhasgradient&y-intercept→smallestsfis3sf

○ Needunits○ Appliestoproportionalityconstant ● Calculategradient/y-intercept○ 3sf○ Nounits○ “CalculategradientGofthetangent”←questionwantsgradient,notaconstant.Gisaplaceholdertosignifygradient. ● Justifyyoursfgiventoconstant1. Constanthasthesamesignificantfiguresastheleastsignificantfigureofthevaluessubstituted2. (variable)hastheleastsfof()3. Henceconstanthas()sf. ● Calculate%difference○ Useaveragevalueindenominator○ 2sf,like%uncertainty○ %diff>%uncertaintythenresultsdonotsupportsuggestedrelationship ● Table○ Headings:lookatwhatyouareplotting.Followit.○ 22.0is3sf,not2sf.Thezeroafterthedecimalplacetakesup1sf.○ Rangeis80%ofmaximum→means:ifthewholethingis100cm,urrangeshouldbe80cm,eg20-100cm ● Graph○ Labelingofaxis:ifthereare2variables,addabracket. ✔(m2 -m1 )/g○ Usegraphtofindaspecificvalue:don’tcreatey=mx+cequation.Instead,dothegradientmethod.1)Drawgradienttriangletofindgradient.2) .Subincoordinatesfromapointandvaluethatyouknow. 𝑌1−𝑌2𝑋1−𝑋2 = 𝑔𝑟𝑎𝑑𝑖𝑒𝑛𝑡 Miscellaneous

● Ifcambridgedecidestoshowitstruefuckernatureandmakesurepeatentireexperimentforanewobjectfor2marksordosomethingridiculouslydemanding,whackit,justget2datasets,plotitandfuckoff.● Lastqnmaybeafunkyqntodrawdiagram,suggeststepsofprocedure/howtouseinstrumenttocomparesmth.○ Ifit’stheformer→it’sjustaminiplanning.MarksmaybegivenforthereasonwhyyoumeasureYinsteadofthevariableinquestion.Egthevariableistension,andqnrestrictsutoaspring.Soumeasureextension.Marksgivenforwriting“tensionproportionaltoextension”.○ Ifit’sthelatter→manymarks:1mforhowtheinstrumentisused,howtoinfer.Othermarksareforadditionaldetails. Planning (a)Measure(b)Vary(c)Control Methodologyforplanning1. Circleimportantstuffinqna. Egyouaretaskedtoproduceicecubesat0 0 C←needtousetemperaturesensorconnectedtodatalogger2. Linearizeequation.Logbothsides.3. Identifyindependent,dep&2-3controlvar.4. Thinkofequipmentusedtomeasure5. Proceduretovaryandcontrolstuff6. Scrutinizegivendiagram,think:WhatwillPatrickJaneobservethatIhaven’tyetnoticed?→additionaldetails

Presentyourwondrousexperimentation1. Header:Experiment1:VaryxwhilekeepingYconstant2. “Setupasshownindiagramabove.”3. Createobjectforexperimenta. Additionaldetails(fromstep6above)4. Insertpreliminaryreadings5. Measurementmethodsfordependent&independentvariablesa. Repeatmeasurementsindifferentpositionsandtakeaverageb. Methodtomeasure/calculate,ifthevariablescannotbeobtaineddirectly.i. Egextension:measure2lengths,L0andL1.Extension=L1-L0.ii. Egnumberofoscillations:placeafiducialmarkertomarkoutequilibriumposition.Countoscillationseverytimeobjectpassesfiducialmarker?6. ProceduretovaryindepvarX7. ProceduretokeepYconstant8. Proceduretokeepconstantsconstant9. Analysisofdataa. “Plotagraphof…Iftherelationshipisvalid,astraightlinegraphofgradient…willbeobtained.”Thereisnoneedtowrite“Tabulate(variables)”10.Additionaldetails&safetyprecautions Notes● Ifyouarestuckatthemeasuringpart,put“xxxsensorconnectedtodatalogger”● Ifyouarerunningoutoftime/stuck,writedownadditionaldetailsandpraytogod● Drawurtable.Nofloating.● Includecalculationstoobtainquantityifitcannotbemeasured.Egradius.Measurediameteranddivide2.● Remembertorepeatprocedureandcollect10setsofdataandrepeatmeasurementsfortime,diameteretc Procedures● Moveanobjectatconstantspeed:variablespeedmotorconnectedtopowersupply● Dropanobjectwith0initialv:useelectromagnet.Ironcoreconnectedtoelectricalcircuit.Oncetheswitchisopen,currentstopsflowing,andtheironcoreiseasilydemagnetized.● UniformBfield:usehelmholtzcoils

● Heatingsource:electricalheatingelement Additionaldetails● Preliminaryreadings○ “Takepreliminaryreadingsforbiggestandsmallest(variableX),suchthatconstant(variableY)canbeachievedforallrangesof(variableX)whenvarying(variableX).● Bfield○ Usingacompasstomeasureangleofdeflection:EnsureBfieldofobjectisperpendiculartoBfieldofEarth.BfieldofEarthisusedasareferencepoint.○ EnsuretherearenoexternalBfieldsandferromagneticmaterials○ Usingmagneticfieldsensorconnectedtodatalogger/hallprobe:adjustitinthemagneticfieldsothatthelargestreadingisread.Keeptheapparatusinthisorientationandlocation.● Thermal○ Tokeepsurroundingtemperatureconstant,performexptinairconroom○ Toensureconstantheatsupplied:electricalheatingsystemwithconstantcurrentandvoltage○ Ifthermometerisused:ensurebulbofthermometerisfullyimmersedinliquidandnottouchingside/bottomofcontainer● Oscillations○ RecordtimetakenforNoscillationssuchthatNT>20s.FindperiodTbydividingbyN.○ Fiducialmarker○ Plumbline○ Usewindshieldaroundexperimentset-uptopreventwindfromaffectingoscillation○ Setsmalloscillationstoensureobjectoscillatesinthedesiredplaneanddoesnotwobble.● Apparatus○ Ifyoufindurselfthinking“howdoIknowwhentheexpthasended”,useasensor.Eghowtotellicehascompletelymelted→temperaturesensorconnectedtodatalogger→timingstopsoncetemperaturestopsdecreasing.Eghowtotellwirehasmelted→currentsensorconnectedtodatalogger→timingstopsoncenocurrentisdetected.● Motion○ Recordexperiment,playbackinslowmotion Safetyprecautions:

● Electrical○ Openswitchinbetweenreadingstopreventoverheatingofwires,sothatresistanceandthusammeterandvoltmeterreadingsarenotaffected○ Wearrubberglovestopreventelectrocutionfromhighvoltage/current● Thermal○ Wearrubberglovestopreventburns○ Useholderstopickuphotobjecttopreventburns○ Turnoffheatsourcebetweenmeasurementstopreventburns● Oscillation○ Standfarawayfromoscillatingpathofobjectsothatobject